Relationship between spatial distribution of chaetognaths and oceanographic conditions off Concepción Bay, Chile

Abstract

The composition, and the temporal vertical and horizontal distribution of chaetognaths off Concepción Bay, Chile were analyzed from 15 oceanographic stations along three sections perpendicular to the coast in April, June, November and December 1991. Oblique zooplankton tows, using 60-cm diameter Bongo nets with 350-μm mesh, were carried out to a maximum of 200 m depth. Additionally, in November and December, in the three coastal most stations of each section, stratified vertical zooplankton tows were performed in three strata (25–0, 50–25 and 100–50 m) with a WP-2 net, with 350-μm mesh provided with a flowmeter to determine the filtered volume. The community of chaetognaths showed ten species: Sagitta enflata, S. bierii, S. decipiens, S. tasmanica, S. lyra, S. minima, S. planctonis, Krohnitta subtilis, K. pacifica and Eukrohnia hamata. Of these species, S. enflata was the most abundant and frequent in both vertical and oblique samples. In vertical samples, some mesopelagic species were identified, such as E. hamata, S. decipiens, S. lyra and S. planctonis. These species were more abundant in November, when the upwelling was more intense. An inverse situation was observed in December, when the abundance of S. enflata, an epiplanktonic species, increased, associated with greater water-column stability. With exception of S. enflata, the other species had not been previously recorded in the vicinity of Concepción Bay.